The present invention relates to polymer nano-particles, a method for their preparation, and their use as, for example, additives for rubber, including natural and synthetic elastomers.
Polymer nano-particles have attracted increased attention over the past several years in a variety of fields including catalysis, combinatorial chemistry, protein supports, magnets, and photonic crystals. Similarly, vinyl aromatic (e.g. polystyrene) microparticles have been prepared for uses as a reference standard in the calibration of various instruments, in medical research and in medical diagnostic tests. Such polystyrene microparticles have been prepared by anionic dispersion polymerization.
Nano-particles can be discrete particles uniformly dispersed throughout a host composition. Nano-particles preferably are monodisperse in size and uniform in shape. However, controlling the size of nano-particles during polymerization and/or the surface characteristics of such nano-particles can be difficult. Moreover, achieving better control over the surface composition of such polymer nano-particles also is desirable.
Rubbers may be modified by the addition of various polymer compositions. Such polymeric additives often improve the physical properties of rubber compositions. Specifically, moldability and tenacity are often approved through such modifications.
Development of nano-particles having a poly(conjugated diene) surface layer which would be compatible with a wide variety of rubbers is desirable because discrete particles could likely disperse evenly throughout the rubber to provide a uniform rubber composition. However, the solubility of diene monomers in traditional alkane solvents has made solution polymerization a difficult process by which to achieve conjugated diene nano-particles.
A polymer nano-particle composition is provided. The nano-particle includes a crosslinked poly(alkenylbenzene) core and a surface layer including poly(conjugated diene). The mean average diameter of such polymer nano-particles is preferably less than about 100 nm.
A method for forming polymer nano-particles is also provided. Alkenylbenzene monomer and conjugated diene monomer are copolymerized in a hydrocarbon solvent to form a diblock polymer. A crosslinking agent, optionally with a further vinyl-substituted aromatic hydrocarbon monomer and/or a conjugated diene monomer charge, is added to the polymerization reaction to form the nano-particles.
In another embodiment, a rubber composition is formed, wherein the above-described nano-particles are combined with at least one rubber to form a modified rubber composition with improved tensile and/or tear strength.
Herein throughout, unless specifically stated otherwise:
xe2x80x9cvinyl-substituted aromatic hydrocarbonxe2x80x9d and xe2x80x9calkenylbenzenexe2x80x9d are used interchangeably; and
xe2x80x9crubberxe2x80x9d refers to rubber compounds, including natural rubber, and synthetic elastomers including styrene-butadiene rubber, ethylene propylene rubber, etc., which are known in the art.